The piano is a musical instrument played by depressing keys laid out sequentially on a keyboard. In traditional pianos, pressing a key causes a felt-covered hammer to strike steel strings and thereby produce a pitched tone. The hammers rebound, allowing the strings to continue vibrating at their resonant frequency, and these vibrations are transmitted through a bridge to a sounding board that amplifies the volume of the sound. In electronic instruments having keyboards, pressing a key results in the playing of a predetermined sound associated with that key by the electronic instrument.
The layout of keys on a piano keyboard has been standardized in order to allow players to more easily play repertoire learned on different instruments. The spacing between the keys of a standard piano has changed little since the 18th century.